Nutrient Cycling in Soil Cores with Different Native and Exotic Earthworms.

Earthworms are ecosystem engineers and can alter ecosystem functioning. The introduction of non-native species, including non-native earthworms, into different ecosystems has implications for ecosystem functions, such as nutrient cycling. The plant community, and its interactions with microorganisms, also impacts nutrient cycling through its surface and belowground inputs. Endophyte infection (Neotyphodium coenophialum) of grasses can alter soil microbial biomass and C and N dynamics. It is important for the understanding and management of grassland ecosystems to determine how integration of these components impacts nutrient cycling. Therefore, the objective of this study was to determine if C and N derived from fescue litter is cycled differently in the presence, absence, or combined presence of native and non-native earthworms. A laboratory incubation was conducted using 10-cm dia., 30-cm long PVC cores filled with 20 cm of Captina silt loam growing unlabeled toxic endophyte-infected tall fescue with ¹⁵N-labeled tall fescue litter on the soil surface. Treatments include a no-worm control, cores with two Diplocardia sp. (native worms), cores with two Aporrectodea trapezoides (non-native worms), and cores with Diplocardia sp. and Aporrectodea trapezoides. Microbial, dissolved and total soil C and N concentrations were measured along with ¹⁵N concentrations in the soil, worms, and fescue for up to 22 weeks after litter additions. We are investigating whether changes in community composition from native worms to native plus non-native earthworms result in altered nutrient cycling and availability. These results are important in ecosystems where non-native worms are introduced.